In recent years, high integration and high density in semiconductor device demands smaller and smaller wiring patterns or interconnections and also more and more interconnection layers. Multilayer interconnections in smaller circuits result in greater steps which reflect surface irregularities on lower interconnection layers. An increase in the number of interconnection layers makes film coating performance (step coverage) poor over stepped configurations of thin films. Therefore, better multilayer interconnections need to have the improved step coverage and proper surface planarization. Further, since the depth of focus of a photolithographic optical system is smaller with miniaturization of a photolithographic process, a surface of the semiconductor device needs to be planarized such that irregular steps on the surface of the semiconductor device will fall within the depth of focus.
Thus, in a manufacturing process of a semiconductor device, it increasingly becomes important to planarize a surface of the semiconductor device. One of the most important planarizing technologies is chemical mechanical polishing (CMP). In the chemical mechanical polishing, using a polishing apparatus, while a polishing liquid containing abrasive particles such as silica (SiO2) or ceria (CeO2) therein is supplied onto a polishing pad, a substrate such as a semiconductor wafer is brought into sliding contact with the polishing pad, so that the substrate is polished.
The polishing apparatus for performing the above CMP process includes a polishing table having a polishing pad, and a substrate holding device, which is referred to as a carrier or a top ring, for holding a substrate such as a semiconductor wafer. By using such a polishing apparatus, the substrate is held and pressed against the polishing pad under a predetermined pressure by the substrate holding device, thereby polishing an insulating film or a metal film on the substrate.
After one or more substrates have been polished, abrasive particles or ground-off particles of the substrate are attached to the surface of the polishing pad, and surface topography or surface condition of the polishing pad is changed, resulting in deterioration in polishing performance. Therefore, as the substrates are repeatedly polished by the same polishing pad, a polishing rate is lowered and nonuniform polishing action is caused. Thus, dressing (conditioning) of the polishing pad is performed by using a dresser to regenerate the surface topography or surface condition of the polishing pad which has deteriorated.
In CMP (Chemical Mechanical Polishing), the surface topography and surface condition of the polishing pad have a large effect on the polishing performance, and thus it has been proposed to measure the surface topography and surface condition of the polishing pad by various measuring methods.
For example, Japanese Laid-open Patent Publication No. 9-119822 discloses a method for measuring the surface roughness of the polishing pad by applying a light beam to a polishing pad.
Further, Japanese Laid-open Patent Publication No. 2014-172153 discloses a method for measuring the surface properties of the polishing pad by applying a laser beam to the polishing pad and obtaining a spatial wavelength spectrum from scattered light reflected and scattered by the polishing pad.
None of prior art documents including Japanese Laid-open Patent Publication No. 9-119822 and Japanese Laid-open Patent Publication No. 2014-172153 addressed to the measurement of the surface roughness, surface properties, etc. of the polishing pad surface, refer to a technology for applying a light beam such as a laser beam to the polishing pad at a plurality of incident angles.
The present inventors have repeated experiments in which a laser beam is applied to a polishing pad to evaluate the surface properties of the polishing pad and have analyzed the results of the experiments. As a consequence, the present inventors have found such a problem that if the surface properties of the polishing pad are not measured using a plurality of incident angles, there are instances in which the surface properties of the polishing pad that truly reflect CMP performance cannot be captured.